Effect of catalyst precursor and its pretreatment on the amount of β-Pd hydride phase and HDS activity of Pd-Pt/silica-alumina

Abstract

The effect of catalyst precursor and pretreatment on the content of β-Pd hydride (PdHx) and activity of the reduced bimetallic Pd-Pt catalysts in hydrodesulfurization (HDS) of thiophene and benzothiophene was studied. The catalysts prepared by co-impregnation of mesoporous silica–alumina (MSA) by different metal compounds were characterized by nitrogen, hydrogen, CO adsorption, chemical analyses, electron-probe microanalysis (EPMA) and temperature-programmed hydride decomposition (TPHD). It was found that metal precursor and its pretreatment greatly affected the properties of the catalysts. The most active catalysts were prepared from Pd acetate and Pt(NH3)4(OH)2. Strong Brønsted acidity of the support led to the highly active and sulfur tolerant catalysts. About 20% of the active phase surface remained in the metallic state after thiophene HDS. The reduced Pd-Pt/MSA catalysts absorbed hydrogen in the form of PdHx phase. Its amount was greatly affected by the precursor, its pretreatment and overall metal dispersion. A relation between thiophene HDS activity and the amount of hydrogen present in the PdHx was observed within the whole series of Pd-Pt catalysts. This shows that the hydrogen accumulated in the bulk of Pd participated in the reaction along with the hydrogen activated on the catalyst surface and positively contributed to the overall thiophene transformation over Pd-Pt/MSA catalysts.